Offer products or services for bitcoins, the marketplace forum is a good place to start if you take that approach. To deal with the trust issue consider using a escrow service such as clearcoin. https://clearcoin.appspot.com/

Use one of the exchanges to buy some. Mt.Gox is the largest. You can get funds in through Dwolla or Liberty Reserve. Dwolla is simpler and cheap but slow. I don't know how fast Liberty Reserve is looked too complicated to bother with when I looked at it.

Use you computer power to help secure the bitcoin network and earn bitcoins in exchange. The mining forum has more information about that. It requires high end GPU(s) preferably AMD ones and some technical knowledge. If you want earnings at a slow and steady rate rather than large amounts rarely you need to join a mining pool.

If you're in the US, follow these steps for the fastest way to get Bitcoin:

1) Create a free exchange account with MtGox.com or CryptoXChange.com (5 mins)2) Go to BitInstant and create a cash deposit order (5 mins)3) Drive to a local bank branch of Bank of America, Chase, Citi, or Wells Fargo (you don't need an account with them) (15 mins)4) Deposit your cash according to the instructions from BitInstant (5 mins)

Then, probably before you even get home, you'll have credit in your exchange account to buy Bitcoins. You can literally have the Bitcoins an hour from now. Of all the ways to get Bitcoin, this is by far the fastest and easiest.

Using an exchange is likely the most common way people get bitcoins. Exchanges are business that broker trades between people. The buyers and sellers using the exchange set the rates by putting in an order to buy or sell.